Sintered, porous materials made of, for example, ceramics or metals, have many uses in a variety of fields, including the fields of industry and medicine. Certain porous sintered structures can serve as filters, for example, whereas others may serve as bone substitute materials. Sinterable particles of various types may be molded, with or without the presence of organic binders, into a desired shape and then fired to remove the binder and to cause the particles to flow into each other at their points of contact. Preformed polymeric structures such as sponges and the like may be infused with a ceramic slip, dried, and fired to remove the organic support and to sinter together the ceramic particles, all for the purpose of manufacturing materials having reasonably large size pores and which are suitable for use as bone substitute materials. Reticulated structures of this kind have the advantage over other porous structures in that there is a three dimensional open continuum without openings being blocked. Thus, full advantage is taken for any merit that porosity confers such as having a fully available internal surface area.
In conventional sintered materials such as ceramic bodies, structures free of pores are normally desired. In the early stages of sintering or consolidation, pores in the structure are largely open from one pore to the next, but the structure is weak. As sintering proceeds, the pores become increasingly smaller and eventually are closed as they are filled by various sintering mechanisms such as diffusion. When a sintered body is about 90% dense, nearly all the pores are closed and thus are isolated from one another.
In general terms, the strength of a sintered body increases as porosity decreases. Conventional methods of making porous bodies involve the use of foaming agents, or the use of particulate materials that can be burned out, but interconnections between the resulting pores are usually far from complete. Connections leading to a more open porosity increase with greater pore formation; hence, resulting in less solid materials with thinner walls and leading to weak structures. These processes have been applied to making closed pore media useful for thermal insulation. Where very fine pores are needed, strength is sacrificed as is the degree of porosity available.